From what I can see iD have been an engine company since the days of Quake, it just so happens that they occasionally release a game to show off the new engine

From what I can see iD have been an engine company since the days of Quake, it just so happens that they occasionally release a game to show off the new engine they're peddling. That doesn't make Carmack any less of a great developer in how he pushes the limits of current hardware.